Field of the Invention
The invention relates to an optical system, and more particularly to an optical system with small perspective distortion and an ultra-wide angle.
Description of the Related Art
At present, optical camera lenses for use in cars or conferences generally have the following disadvantages: large lens distortion, large perspective distortion, low resolution, insufficient field angle, and the like.
Perspective distortion refers to a scenario in which obvious dissymmetry occurs in images at edges during photographing a three-dimensional object. For example, as shown in FIG. 2, according to basic principles of imaging, when imaging a square frame AE, the AE is in the same plane; a midpoint of AE is set as O, so its projection A′E′ is also equally divided by a midpoint O′. Therefore, a proportion relation appears to be correct and symmetrical. However, for a three-dimensional object such as a sphere (as shown in FIG. 3), although a sphere is circularly symmetrical, at edges of a field, AB is projected and imaged to be A′B′ for the sphere during projection imaging. The physical length corresponding to AO is CO, and the physical length corresponding to BO is DO. Although CO and DO are both equal to a radius of the sphere, for the projections of CO and DO, BO is far greater than AO; and the asymmetric effect becomes more obvious at a further edge of the field, and further in the projected image, B′O′ is also greater than A′O′.